1. Field of the Invention
This invention relates to compositions which are capable of stabilizing rigid (unplasticized) halogen-containing organic polymers against the deteriorative effects of heat, light and weathering. Such stabilizers comprise an organotin mercaptide and/or an organotin sulfide, and a dialkyl ester of an ethylenically unsaturated dicarboxylic acid. The invention also relates to halogen-containing organic polymers stabilized with such compositions.
2. Description of the Prior Art
It has long been known that halogen-containing organic polymers, such as the commercially important poly (vinyl chloride), are subject to deterioration or degradation when exposed to heat and light. Various chemical compounds and compositions have been developed to stabilize these polymers against such deterioration. For the most part, these stabilizers have been directed toward stabilization against heat, such as that encountered during processing of the polymer and its fabrication into articles. Among these heat stabilizers, some of the most effective have been the organotin compounds. The organotin compounds which have been found to be effective heat stabilizers for halogen-containing organic polymers include a wide variety of compounds. Mono- and dialkyltin carboxylates and mono- and dialkyltin mercaptides, for example, have been employed successfully as heat stabilizers.
Other organic, non-metallic compounds have also been found to be useful as heat stabilizers for halogen-containing organic polymers and are sometimes employed in combination with the organotin stabilizers. For instance, U.S. Pat. No. 3,379,679 discloses stabilizer compositions containing an organotin maleate of the formula: ##STR1## and a maleate ester of the formula: ##STR2## where R, R.sub.1 and R.sub.2 are each alkyl or alkenyl of up to 12 carbon atoms, or aryl, alkaryl or aralkyl of from 6 to 9 carbon atoms; and R.sub.3 is hydrogen, alkyl or alkenyl of up to 12 carbon atoms, or aryl alkaryl or aralkyl of from 6 to 9 carbon atoms, provided that at least one of said R.sub.3 is other than hydrogen.
With the increased use of halogen-containing organic polymers for rigid articles which will be exposed to light and weathering for long periods of time (e.g. housing siding and window profiles) it has become increasingly important to develop a stabilizer which will not only protect the polymer against the high temperatures encountered during processing and fabrication, but will also protect the polymer against the long-term effects of light and weathering. However, until the present invention, no single stabilizer composition was completely satisfactory for protecting the halogen-containing organic polymers against heat, light and weathering. Thus, while an organotin compound, and in particular the organotin mercaptides, provided good heat stability, they were not acceptable weathering stabilizers. Likewise, the aforementioned combination of organotin maleates and maleate esters disclosed in U.S. Pat. No. 3,379,679 does not provide adequate heat stability, is incompatible with normally used ingredients employed in commercial polymer formulations (commonly called "microingredients"), such as calcium stearate, and can cause problems with eye irritation and offensive odors due to the presence of the organotin maleate. Thus, the industry has been unable to use organotin maleates as light stabilizers because of the aforementioned problems. Instead, it chooses to use the organotin mercaptides which overcome the problems of eye irritation and incompatibility with microingredients, but which give less than desired weathering and light stabilization.
It has now been quite unexpectedly discovered that the problems encountered with the prior art stabilizers can be overcome while still providing excellent stabilization of halogen-containing organic polymers against heat, light and weathering when stabilizers are employed which comprise organotin sulfides, organotin mercaptides and/or organotin carboxylates in combination with dialkyl esters of ethylenically unsaturated dicarboxylic acids.